#include <assert.h>
#include <stdio.h>
#include <string.h>

char* my_strcat(char* dest, const char* src) {
    assert(dest != NULL);
    assert(src != NULL);
    char* p = dest;
    while(*dest) {
        dest++;
    }
    while((*(dest++) = *(src++))) {
        ;
    }
    return p;
}

int main() {
    char string1[30] = "hello ";
    char string2[] = "world!";
    my_strcat(string1, string2);
    printf("%s", string1);
    return 0;
}